Many aircrafts include main electric power supplies which are electric generators driven by main engines for aircraft, and auxiliary electric power supplies which are auxiliary power units (APU) including electric generators which are driven by auxiliary engines, batteries, and the like.
As an example of the electric generator driven by the main engine, for example, there is an integrated drive generator (hereinafter will be referred to as “IDG”). The IDG is driven by the main engine to generate electric power and supplies the electric power to components within the aircraft, while the main engine is started. Typically, the APU generates electric power and supplies the electric power to the components within the aircraft, in place of the IDG, while the aircraft is parked, and the main engine is deactivated (running of the main engine is stopped). The battery is used to supply minimum and required electric power for a limited time, in a case where the IDG and the APU are not used.
While the aircraft is parked and the IDG and the APU are deactivated, an external ground power unit (GPU) is connected to the aircraft to supply the electric power to the components within the aircraft.
In a case where electric power supply is switched between the plurality of electric power supply sources without instantaneous interruption (temporary blackout), a synchronous power-on/off control is performed. The synchronous power-on/off control is defined as a control for synchronous power-on/off of breakers for switching, in a state in which voltages, frequencies, and phases are substantially equalized between the plurality of electric power supply sources. As an example of techniques for this synchronous power-on/off control, for example, Patent Literature 1 discloses a method and device for synchronous power-on/off.
Patent Literature 1 discloses that a generator drive rotation speed of a transmission provided between an electric generator and an engine for driving the electric generator is feedback controlled so that a frequency difference between the plurality of electric power supply sources is within a predetermined range and a phase difference between the plurality of electric power supply sources is within a predetermined range. With this control, even in a case where the phase difference does no change dynamically (a change in the phase difference stagnates), the phase difference which meets a synchronous power-on/off condition can be quickly realized by positively controlling the phase difference, and this phase difference can be maintained at a value within a predetermined range for a long time. Therefore, the influence of a disturbance can be lessened during the synchronous power-on/off.